The present invention relates to a method and apparatus for sampling gas-entrained particulate materials and more particularly relates to a method and apparatus for sampling gas entrained particulate materials in which the stream of gas-entrained particulate matter is continuously sampled.
Nylon polymer which is prepared in an autoclave polymerization vessel is ordinarily extruded from this vessel in a molten state, quenched with water for solidification and chopped into pieces known as flake. The extrusion, quenching and chopping steps are often referred to as flake "casting". The flake form of the polymer is readily processed further into other articles such as, e.g., fiber.
Since the autoclave process is a batch process, it is known to be subject to variability which may affect the properties of the flake produced by the process. For this reason, there is a need to sample each batch of flake during a casting process to perform off-line analyses. These analyses may include measurement of polymer viscosity and the determination of amine and/or carboxyl end concentration. The need to collect a flake sample for analysis which accurately represents the material produced in each batch is a well-recognized part of any analytical protocol. That is, a sample of flake must be obtained during the course of extrusion which is representative of the first kilogram of material cast, as well as, the last kilogram of polymer to exit the vessel. It is well-known that a profile of properties, like relative viscosity, may be present in the polymer extruded from the autoclave. By sampling the flake extruded over the approximately 20 minute span of casting, a representative sample of the entire is obtained.
Sampling systems which can be used for nylon flake are commercially available. For example, Intersystems Industrial Products, Inc., 17330 Preston Road, Dallas, Tex. 75252 manufactures the Model PT sampler which grabs flake samples at timed intervals from an air-entrained stream of nylon flake using a solenoid-controlled air cylinder to push a sampling tube into the product stream. A cavity in the sampling tube gathers the sample, the tube is retracted and the sample is eventually conveyed by gravity to a sample container. Using this equipment, samples can be collected at about 30 second intervals during which the sample tube is exposed to the quenched flake stream for about 1 second. Over the course of a typical 20 minute casting run about 40 such samples are obtained which are then pooled to provide a sample of about 300 grams. However, the necessary intervals between each sample means that the pooled sample is not truly representative of the entire flake casting run. Furthermore, such mechanical sampling systems are complex, have a number of moving parts, and require frequent maintenance. The compressed air system containing a high level of stored energy can also be dangerous when repair or adjustment of such samplers is being performed.